1. Field of the Invention
The present invention relates to a method of interlockingly controlling a robot and a positioner with each other and, more particularly, to a method wherein positional data on a teaching/playback robot for welding and on a positioner carrying a workpiece thereon are received thereby permitting a welding operation to proceed while allowing for control of position and speed interlockingly during playback.
2. Description of the Prior Art
FIG. 1 schematically illustrates a welding robot system using a positioner, in which reference numeral 1 denotes a body of a multi-articulate type teaching/playback robot; numeral 2 denotes a robot control panel for controlling the robot body 1; 3 denotes a positioner to which is fixed a workpiece; 4 a positioner control panel for providing a control instruction to the positioner 3 on the basis of a command provided from the robot control panel 2; 5 a welding torch; 6 a welding wire feed device; 7 a welding power source; and 8 a shielding gas. According to the prior art, when performing playback (welding) while moving the robot body 1 and the positioner 3 interlockingly with each other in such a system, first a workpiece is positioned and fixed in a welding position by means of the positioner 3, then after stopping the positioner 3, the robot body 1 is driven to perform a welding operation, and when the welding operation is over and the movable part of the robot body 1 has been retracted to a position not contacting the workpiece, the positioner 3 positions the next workpiece in the welding position. Thus, the welding operation is performed while moving the robot body 1 and the positioner 3 in an alternately manner, that is, the control is not under simultaneous operation of the positioner 3 and the robot body 1.
Moreover, in the case of welding not a simple linear weld line but, for example, a circumferential weld line (particularly when the welding torch 5 is to be faced downward during welding), it is necessary to perform welding while rotating the work. However, according to the prior art, only when the weld line is circular and a workpiece is attached to the positioner 3 so that the center of this circle and the center of rotation of a turntable of the positioner 3 coincide with each other, it has been possible to perform welding while moving the positioner 3 during the welding operation. In this case, the robot body 1 merely remains stationary while maintaining the position and angle of the torch 5 and the turntable of the positioner is merely rotating at a speed determined by the diameter of the weld line (circular) so that the moving speed of the weld line relative to the torch 5 becomes the welding speed. Control is merely such that the rotation of the positioner is started at a predetermined speed with an arc start signal and stopped with a welding end signal. During welding, the robot body 1 and the positioner 3 are maintained under separate control with respect to their relative positional relation and operating speed.
In case the center of rotation of the turntable and the center of the weld line circle deviate from each other, such separate control causes the following drawbacks, as shown in FIG. 2, first, the torch angle relative to the weld line changes, and second, because the amount of deviation in and y directions changes momentarily, the torch may move away too much from the weld line or come too close thereto resulting in contact with a workpiece W. In FIG. 2, the arrow indicates a torch in a fixed position, and FIG. 2(a) shows the case where point (A) is in a position of 0.degree. with respect to a workpiece center O.sub.w, and similarly FIG. 2(b) 45.degree., (c) 90.degree., (d) 135.degree., (e) 180.degree. and (f) 270.degree.. The mark O.sub.p indicates the center of rotation of the positioner, and the workpiece W rotates about this point O.sub.p.
In case the weld line is not circular but instead a complicated curved line such an ellipse or a hyperbola, the above-mentioned drawbacks appear more conspicuously.
According to the conventional teaching method, moreover, a relative position between the robot body and the positioner can be controlled only approximately, and further, as shown in FIG. 2, control of the welding speed is impossible because the radius of gyration of the weld line varies momentarily. This is true especially of a PTP type teaching/playback robot.
In teaching a circumference with a PTP type robot, it is here assumed that, as shown in FIG. 3, a teaching occurs of the position of the torch (shown in arrow in the figure) and that of the positioner P in initial state .circle.1 and then a similar teaching occurs in state .circle.2 . In playback, as shown in FIG. 4, the positional relation between the positioner P and the torch is correct in state .circle.1 and state .circle.2 , but on the way from state .circle.1 to state .circle.2 the target position of the torch deviates from its proper position, as indicated at d.sub.2, d.sub.3, d.sub.4 and h.sub.2, h.sub.3, h.sub.4. The radius of gyration r of the workpiece W also changes from r.sub.1 to r.sub.2, r.sub.3, r.sub.4, r.sub.5. In order to attain a constant welding speed, it is necessary to detect the radius of gyration r continuously and control the rotating speed of the positioner on the basis of the detected r. However, it is difficult to detect the radius of gyration r and hence difficult to control the welding speed. In the illustrations of FIGS. 3 and 4, the positioner P is rotated by 90-deg. But, even in case this angle is made smaller and teaching occurs about many points, the relative positional relation between the positioner P and the torch is merely approximate and hence the welding speed is also merely approximate.